Retroreflective articles have the ability to redirect obliquely incident light back towards the light source. This unique ability has led to the wide-spread use of retroreflective articles on various substrates. For example, retroreflective articles can be used on flat inflexible substrates, such as road signs and barricades; on irregular surfaces, such as corrugated metal truck trailers, license plates, and traffic barriers; and on flexible substrates, such as road worker safety vests, a jogger's shoes, roll up signs, and canvas-sided trucks.
One type of retroreflective article includes beads. Such beaded articles commonly use a multitude of glass or ceramic microspheres to retroreflect incident light. Typically, the microspheres are partially embedded in a support film, and a specular reflecting material is provided between the layer of microspheres and the support film. The reflecting material can be a metal layer (for example, an aluminum coating as disclosed in U.S. Pat. No. 3,700,478 (Bingham '478) and U.S. Pat. No. 4,648,932 (Bailey)), an inorganic dielectric mirror made up of multiple layers of inorganic materials that have different refractive indices (for example as disclosed in U.S. Pat. No. 3,700,305 (Bingham '305) and U.S. Pat. No. 4,763,985 (Bingham '985)) or an organic reflective coating made up of multiple polymer layers that have different refractive indices (for example as disclosed in U.S. Pat. No. 6,172,810 B1 (Fleming et al. '810)).
Categories of beaded retroreflective articles include exposed lens, enclosed lens, and encapsulated lens types. Exposed lens beaded articles have a layer of microspheres, the front sides of which are exposed to the environment. Enclosed lens beaded articles have a protective layer such as a transparent polymer resin contacting and surrounding the front side of the microspheres. Encapsulated lens articles have an air gap surrounding the front side of the microspheres and a transparent film hermetically sealed to a support film to protect the microspheres from water, dirt, or other environmental elements.
Other references involving optical articles include U.S. Pat. No. 5,877,895 (Shaw et al. '895) and U.S. Pat. No. 6,083,628 (Yializis).